Answer: In KMnO₄, Mn is in +7 oxidation state and have all the 3d-orbitals vacant. Mn⁷⁺ ion is surrounded tetrahedrally by four oxide ions. All oxide ions have filled 2p-orbitals. There is transfer of an electron from filled 2p-orbitals of oxide ion to vacant d-orbitals of Mn⁷⁺ ion. Since p-orbitals are ungerade and d-orbitals are gerade, therefore, electron transition from p-orbitals of O^2- to d-orbitals of Mn⁷⁺ ion is Laporte allowed i.e., ΔL = ±1 and also there is no change in spin multiplicity during electronic transition. Therefore, transfer of an electron is Laporte and Spin allowed. Therefore, KMnO₄ is intensely purple in colour.

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